1. Field of Invention
The present invention relates generally to gauges for measuring box end depth and squareness of a shoulder of a joint between two threadably connected sections of drill pipe. More specifically, the present invention relates to gauges of the type described which can be utilized in the field.
2. Description of the Prior Art
In oil exploration operations, drill pipe consists of elongated pipe sections having a hollow bore therethrough. One end, the box or female end, of each section of drill pipe has internally tapered threads while the other or male end of each drill pipe has externally tapered threads. Establishing a relatively rigid and sealable threaded connection between two or more sections of drill pipe is necessary to reach the extensive depths necessary for the exploration for and production of oil and natural gas. The hollow oil drill pipe and connected sections thereof often are required to carry liquids or air down or out of the drill pipe, to assist in lubricating the rotating drill bit and cleaning particle cuttings from the hole.
Joints between adjacent sections of drill pipe must be maintained in as rigid a configuration as possible. It is therefore necessary that the female or internally threaded end of each drill pipe section have a square shoulder that flushly abuts the male or externally threaded end of the immediately adjacent section of drill pipe. These rotary shoulder connections must be smoothly sealed in order that the joint between adjacent sections of drill pipe operate with maximum rigidity and sealing efficiency along the length of the drill pipe.
Rigid joints are essential to the rotation of long lengths of drill pipe. The tapered threaded connection alone cannot maintain sufficient rigidity. Only the mating of the square shoulders of adjacent sections of drill pipe can achieve the desired rigidity. A square shoulder is therefore mandatory for rigidity considerations alone. Loss of a joint results in a highly expensive "fishing" job to obtain pipe sections lost down a drill hole.
Fluids, which can be water alone, water in solution with other chemicals, air, or chemicals, are often placed under relatively high pressures as they are forced down the bore of the drill pipe. The pressures under which the fluids are pumped down the drill pipe make it necessary that each joint between adjacent sections of drill pipe be satisfactorily sealed against loss of any of the liquids and further erosion of the joint. A poor seal between adjacent pipe sections permits dirt and grit to get into the area between the shoulders of adjacent pipe sections, greatly increasing erosion and endangering the connection itself. Again, square shoulders are the best means available for making a better, longer lasting seal.
The shoulders can be refaced to obtain the squareness for proper operation in the field. Heretofore, no easily usable measuring tool has been available in the field to allow for the grinding of the shoulder to establish the appropriate squareness and to measure the total depth of the box remaining. Taking a drill pipe section out of the field for work in a machine shop is an expensive and time consuming proposition that should be avoided, if possible.
As the shoulder of the box or female end of a section of drill pipe is repeatedly ground to establish the proper squareness of shoulder, it will, after the operation has been done a number of times, necessarily shorten the box end, ultimately to a point where insufficient shoulder remains to withstand the forces imposed on the rotating connection between drill pipe sections. Measurement of the total box depth is required, in conjunction with any grinding done to the surface. American Petroleum Institute standards establish a minimum distance for new drill pipe sections, which distance is known as L.sub.bc. The L.sub.bc distance is a known quantity for a given pipe section specification. New pipe is also manufactured with a bench mark formed inside the box end defining the minimum box end depth, beyond which the shoulder cannot be ground. Industry standards would prevent grinding within one sixteenth inch of the bench mark. The bench mark is usually obliterated from pipe sections that have been used. It is therefore necessary to gauge the bench mark. This has not been done previously with any accuracy.
No prior art device measures both the box depth and squareness of shoulder on an oil drill pipe section so that field repairs can be made. Devices adapted to measure the depth of a female portion of a threaded connection are known as seen in U.S. Pat. No. 2,330,453 to C. Smith; U.S. Pat. No. 3,015,892 to E. Stuart; and U.S. Pat. No. 1,543,244 to B. Blood. The gauging device of Smith has an outer casing having a slot formed along the length thereof and measurement indicia or marks formed along the edge of the slot. An inner section or tube of the Smith device is slideably received within the outer casing and has a bore along its length. The bore does not pass all the way through the inner section but terminates at a web. The inner section receives a cylindrical socket in each end thereof which socket in turn receives a male depth gauge plug. A key block affixed to the inner section is moved along the slot of the outer section to measure the depth of penetration of the plug, which plug is threadably inserted into the female portion of the threaded connection to be measured. The measurement is not made with reference to maintaining a square shoulder.
The patent to Stuart is a much less complex variation of the principles shown in the patent to Smith. In Stuart, a threaded male end of an inner rod is threadably connected into the female end of the threaded connection to the ultimate depth of that female connection. An outer rod having a cutout portion is slid over the inner rod and the depth of penetration is read on the outer rod by comparing the outer rod position to the inner rod position. Shoulder squareness is not measured and is not a concern to Stuart.
The patent to Blood measures only the correctness of an internally threaded connection and the taper, specifically with relevance toward standard pipe threads. A relatively sliding gauge is shown that is used to determine whether or not the two gauge members are in a proper alignment for the specific type of thread being measured. Deviation of the indicia on the two gauge members from a set zero point indicate improper taper. Shoulder squareness is not measured.
The prior art relating to apparatus or gauges for testing or measuring the squareness of a shoulder of a work piece having a threaded internal bore include U.S. Pat. No. 2,700,224 to S. Johnson and U.S. Pat. No. 2,630,633 to S. Webb. Johnson would check the squareness of a shoulder with respect to an internally threaded bore. Johnson is specifically applicable to a threaded counterbore within a larger outer bore and, in that respect, a collar having two parallel surfaces is fit into the larger outer bore. The collar gives a reference by which the correctness of the smaller counterbore can be determined.
The Webb patent shows an apparatus for measurement of the squareness of drill pipes. The shoulder is, as was the case in Johnson, measured for squareness relative to the threads of the drill pipe itself. No prior art reference was found that utilizes a throat or tapered inner shoulder existing between the inner termination of the internal threads of a drill pipe and the bore of the drill pipe to align a gauge for measuring squareness of the shoulder and depth of the box end.
U.S. Pat. No. 4,216,585 to Hatter; U.S. Pat. No. 3,170,243 to Williams; and U.S. Pat. No. 1,248,340 to Kinney all show various types of depth gauges, some of which use sliding relationships to establish a depth measurement. Other depth gauges are seen in U.S. Pat. No. 2,179,658 to Gallagher and U.S. Pat. No. 2,650,435 to Kidd. A device that can be used in the field to make a reference mark from which properly torqued connections can be made is seen in U.S. Pat. No. 4,222,174 to Hauk et al. Other types of gauges for measuring thread depth are seen in U.S. Pat. No. 2,200,181 to Lamond and U.S. Pat. No. 2,622,336 to Raout.
From the foregoing, it is seen that a need exists for a simple, easily used field tool for first determining whether a drill pipe shoulder can be squared in the field, and second for measuring the shoulder squareness. Combining a tool for measuring and/or seeing the squareness of a shoulder in order to modify the shoulder, while also determining whether sufficient box end depth remains to make the modification, has not been shown. As previously stated, box end depth must be known to allow for precise connection between drill pipe and to make sure sufficient pipe shoulder exists so that adjacent sections of drill pipe can be rigidly connected and sealed.